1. Field of the Invention
The present invention relates to a lens barrel used for a zoom lens and the like, and to an optical apparatus with a lens barrel such as a video camera.
2. Description of the Prior Art
An example of a prior art zoom lens for a video camera comprises the following four lens components: a fixed positive lens component, a movable negative lens component, a fixed positive lens component, and a movable positive lens component, which are disposed in this order starting from the object side. However, zoom lenses of other various configurations are also known.
FIG. 12(A) and FIG. 12(B) are diagrams showing the configuration of a zoom lens barrel according to the prior art. The zoom lens comprises the following four lens components 201a-201d: a fixed front lens compornent 201a; a variator lens component 201b for moving along the optical axis and thereby varying power; a fixed afocal lens component 201c; and a focusing lens component 201d for moving along the optical axis and thereby performing focal plane maintenance and focusing at power variation.
The front lens 201a is held in a front lens barrel 202. The variator lens component 201b is held in a variator moving ring 211. The afocal lens component 201c is held in a middle frame 215. The focusing lens component 201d is held in a focus moving ring 214.
The focus moving ring 214 is supported by guide shafts 204a and 204b which are engaged in the holes of a rear barrel 216 and in the holes of the middle frame 215 positioned by the rear barrel 216, whereby the focus moving ring 214 can move forward and backward in the direction of the optical axis.
The front lens barrel 202 is fixed on the rear barrel 216. A guide shaft 203 and a guide screw shaft 208 are supported between the front lens barrel 202 and the rear barrel 216, whereby the variator moving ring 211 is supported such as to be movable forward and backward in the direction of the optical axis. Further, the front lens barrel 202, the middle frame 215, and the rear barrel 216 constitute the outer shape of a substantially sealed lens barrel.
More detailed configurations are as follows. The guide bar 203, 204a, and 204b are disposed parallel to the optical axis 205, and thereby guides the movable lens components and prevents the rotation thereof. A DC motor 206 is a driver for driving the variator lens component 201b. In the figure, the DC motor is used as the driver for the variator lens component. However, a step motor may be used instead, similar to the driver for driving the focusing lens component as described later.
The variator lens component 201b is held in the variator moving ring 211. The variator moving ring 211 has: a press spring 209; and a ball 210 engaged in a screw groove 208a formed in a screwed shaft 208, by a force from the press spring 209. When the motor drives and revolves the screwed shaft 208 via an output shaft 206a and a gear series 207, the variator moving ring 211 moves along the guide shaft 203 in the direction of the optical axis.
The focusing lens component 201d is held in the focus moving ring 214. A sleeve portion (a portion engaged in the guide shaft and thereby forming a guiding portion) in the focus moving ring 214 is provided with a screw member 213 in the form of a single piece. When a step motor 212 is energized and an output shaft 212a thereof revolves, the screw portion formed in the output shaft 212a and the screw portion formed in the screw member 213 work together in linkage with the revolution, whereby the focus moving ring 214 moves along the guide shafts 204a and 204b in the direction of the optical axis.
As described above, such a linkage mechanism with the step motor may be used also in the variator driving mechanism.
In a case where the lens component is moved by such a step motor, when a photo-interrupter (not shown) is provided in order to detect the absolute position of the movable lens component in the direction of the optical axis, and when light blocking wall are provided in the moving ring in the form of a single piece, a reference position of the moving frame in the direction of the optical axis can be detected. After the holding frame is positioned at the reference position, the number of driving steps supplied to the step motor is counted continuously. As such, a position detecting means is obtained for detecting the absolute position of the holding frame.
FIG. 13 is a block diagram showing the electrical configuration of the camera body of an imaging apparatus according to the prior art. In the figure, identical numerals to FIG. 12 indicate identical components having the same function.
Numeral 221 indicates a solid state image device such as a CCD. Numeral 222 indicates a driver for a variator lens component 201b. This includes: a motor 206; a gear series 207 and a screwed shaft 208 in linkage with the motor 206; and the like as shown in FIG. 12. This driver is composed of a step motor or the like similar to the driver for the focusing lens component as shown in FIG. 12. Numeral 223 indicates a driver for a focusing lens component 201d. This includes: a step motor 212; a male-screwed output shaft 212a thereof; a screw member 213 formed in a focus moving ring 214; and the like.
Numeral 224 indicates an iris driver. Numeral 225 indicates a zoom encoder, while numeral 227 indicates a focus encoder. These encoders detect the absolute positions of the variator lens and the focusing lens component, respectively, in the direction of the optical axis. In a case where a DC motor (not shown in FIG. 13) is used in the driver for the variator lens similar to the case of FIG. 12, an absolute position encoder such as a variable resistor may be used. Alternatively, a magnetic absolute position encoder may be used.
In a case where a step motor Is used in the driver, generally used is the above-mentioned method wherein the holding frame is positioned at a reference position at first, and that the number of pulses inputted into the step motor is counted continuously.
Numeral 226 indicates an iris encoder. In an example of this encoder, a Hall device is provided inside a meter serving as an iris driver, whereby the relative rotational position is detected between the rotor and the stator.
Numeral 228 indicates a camera signal processing circuit for performing predetermined amplification and gamma correction for the CCD output. The contrast signal of the video signal that undergoes these predetermined processes is provided to an AE gate 229 and an AF gate 230. In these gates, the regions of signal extraction for exposure determination and focusing are set at an optimum within the field of view. The size of each gated region may be variable. Alternatively, a plurality of regions may be used in each gate. However, a detailed description is omitted for simplicity.
Numeral 231 indicates an AF signal processing circuit for automatic focusing (AF), which generates output signal(s) with respect to high frequency components of the video signal. Numeral 233 indicates a zoom switch. Numeral 234 indicates a zoom tracking memory for storing the information on the focusing lens position to be adopted depending on the object distance and the variator lens position at power variation. The zoom tracking memory may be implemented by a memory in a CPU. Numeral 232 indicates a CPU.
In the above-mentioned configuration, for example, when the zoom switch 233 is operated by a user, in order to maintain a predetermined positional relation between the variator lens and the focusing lens calculated on the basis of the information stored in the zoom tracking memory 234, the CPU 232 controls the driving of the zoom driver 222 and the focusing driver 223 so that the present absolute position of the variator lens in the direction of the optical axis detected by the zoom encoder 225 coincides with the calculated optimum position for the variator lens, and that the present absolute position of the focusing lens in the direction of the optical axis detected by the focus encoder 227 coincides with the calculated optimum position for the focusing lens, respectively.
At automatic focusing operation, the CPU 232 controls the driving of the focusing driver 223 so that the output of the AF signal processing circuit 231 is at peak. For the purpose of optimum exposure, the CPU 232 controls the driving of the iris driver 224 and thereby controls the aperture size in a manner where the average of the Y signal output from the AE gate 229 becomes a predetermined value, and where the output of the iris encoder 226 becomes the predetermined value.
As described above, a lens barrel according to the prior art has been composed of: a fixed positive lens component held in a fixed barrel; a movable negative lens component supported by two guide shafts such as to be movable forward and backward in the direction of the optical axis; a fixed positive lens component held in a middle frame; a movable positive lens component supported by two guide shafts such as to be movable forward and backward in the direction of the optical axis; and a CCD at a final image plane held in a rear barrel; which are disposed in this order starting from the object side. Further, the movable negative lens component and the movable positive lens component have been enclosed in the fixed barrel and the rear barrel, respectively. And, a substantially sealed lens barrel structure has been formed by the fixed barrel, the middle frame, and the rear barrel, or alternatively by the fixed barrel and the rear barrel.
In recent years, size reduction and diameter reduction have been demanded in picture lenses. Nevertheless, in particular, when the outer diameter of the fixed barrel is reduced, an inner wall reflection ghost occurred in which reflected light from the inner wall of the barrel reaches the image plane.
This has created a requirement for a light blocking means such as light blocking lines in the inner wall of the fixed barrel. Nevertheless, in a lens barrel configuration according to the prior art, when light blocking lines are provided in the inner wall of the fixed barrel, the mold used for molding the lens barrel becomes complicated. For example, the mold configuration becomes a very complicated one in which the molding is carried out after the light blocking portion is slid inward. This has created a problem of an expensive and non-durable mold. Further, the method has been applicable only to lens barrels of a larger inner diameter, and hence not applicable to fixed barrels of a reduced size. These problems have prevented the size reduction of lens barrels.
Thus, in order for the light blocking lines to be easily molded, a box-shaped lens barrel configuration in which one side surface of a box-shaped lens barrel body is set to be an opening surface, and in which movable lens components are built-in by passing through the opening and then the lens barrel is sealed with a cover is proposed. Nevertheless, in a case of such a box-shaped lens barrel, from the viewpoint of easy assembling, support for the guide shafts for positioning and supporting the movable lens components and the middle frame requires a semicircular shape facing the opening surface. Accordingly, the guide shafts need to be fixed with the cover. Nevertheless, insufficient rigidity of the cover material has caused an instability in the fixture of the guide shafts. This, in turn, has caused pickup of drive motor vibrations and resonance with it, and thereby an exacerbation in acoustic noise and the like.
An object of the invention is to provide a lens barrel in which enclosed movable lens component frames and fixed lens component frames are assembled more easily, and in which guide shafts are stably fixed for positioning and supporting the movable lens components and the fixed lens components in a manner in that the movable lens components are movable in the direction of the optical axis.
In order to achieve the above-mentioned object, an aspect of the invention is a lens barrel comprising:
a lens unit having an optical axis and forming an optical image, said lens unit having a fixed lens component and a movable lens component; and
a lens housing for containing said lens unit, said lens housing having a first housing and a second housing divided in a direction along said optical axis.
Another aspect of the invention is a lens barrel comprising:
a lens unit having an optical axis and forming an optical image, said lens unit having: a plurality of fixed lens components including a front fixed lens component disposed on the most object side; and a plurality of movable lens components; and
a lens housing for containing said lens unit, said lens housing having a first housing and a second housing divided in a direction along said optical axis; wherein:
in the front portion of said first housing, said first housing has a flange into which said front fixed lens component is fixed;
inside said first housing, said first housing has a lens-holding portion for holding said fixed lens component other than said front fixed lens component; and
said second housing has a pickup-device holding portion for holding an image pickup device for taking said optical image obtained by said lens unit.
Another aspect of the invention is a lens barrel comprising:
a lens unit having an optical axis and imaging an optical image, said lens unit having: a plurality of fixed lens components including a front fixed lens component disposed on the most object side; a plurality of movable lens components; and a guide bar for guiding said movable lens components and for positioning said fixed lens component other than said front fixed lens component;
a lens housing for containing said lens unit, said lens housing having a first housing and a second housing divided in a direction along said optical axis; wherein:
in the front portion of said first housing, said first housing has a flange into which said front fixed lens component is fixed;
inside said first housing, said first housing has: a first guide-bar supporting portion for supporting said guide bar: and a lens-holding portion for holding said fixed lens component other than said front fixed lens component; and
said second housing has: a second guide-bar supporting portion for supporting said guide bar; and a pickup-device holding portion for hoding an image pickup device for taking said optical image obtained by said lens unit.
Another aspect of the invention is an optical apparatus with a lens barrel comprising:
a lens unit having an optical axis and forming an optical image, said lens unit having a fixed lens component and a movable lens component;
an image pickup device for taking said optical image obtained by said lens unit; and
a lens housing for containing said lens unit, said lens housing having a first housing and a second housing divided in a direction along said optical axis; wherein:
said first housing has a lens-holding portion for holding said fixed lens component; and said second housing has a pickup-device holding portion for holding said image pickup device.
Another aspect of the invention is an optical apparatus with a lens barrel comprising:
a lens unit having an optical axis and forming an optical image, said lens unit having: a plurality of fixed lens components including a front fixed lens component disposed on the most object side; and a plurality of movable lens components;
an image pickup device for taking said optical image obtained by said lens unit; and
a lens housing for containing said lens unit, said lens housing having a first housing and a second housing divided in a direction along said optical axis; wherein:
in the front portion of said first housing, said first housing has a flange into which said front fixed lens component is fixed;
inside said first housing, said first housing has a lens-holding portion for holding said fixed lens component other than said front fixed lens component; and
said second housing has a pickup-device holding portion for holding said image pickup device.
Another aspect of the invention is an optical apparatus comprising:
a lens unit having an optical axis and forming an optical image, said lens unit having: a plurality of fixed lens components including a front fixed lens component disposed on the most object side; a plurality of movable lens components; and a guide bar for guiding said movable lens components and for positioning said fixed lens component other than said front fixed lens component;
an image pickup device for taking said optical image obtained by said lens unit; and
a lens housing for containing said lens unit, said lens housing having a first housing and a second housing divided in a direction along said optical axis; wherein:
in the front portion of said first housing, said first housing has a flange into which said front fixed lens component is fixed;
inside said first housing, said first housing has: a first guide-bar supporting portion for supporting said guide bar; and a lens-holding portion for holding said fixed lens component other than said front fixed lens component; and
said second housing has: a second guide-bar supporting portion for supporting said guide bar; and a pickup-device holding portion for holding said image pickup device.
Further objects and configurations of the invention are clearly disclosed in the following description of the embodiments.